1. Field of the Invention
The present invention relates to a magnetic recording method, a magnetic tape and a magnetic recording and reproducing method.
2. Description of the Prior Art
As a video tape recorder (VTR) for recording and reproducing a video signal, a VTR of the VHS system has been well known. In such VTR, a video signal is recorded on slant tracks formed on a magnetic tape obliquely to a longitudinal direction of the magnetic tape by utilizing rotary video heads mounted on a rotary drum and an audio signal is bias-recorded on a track formed on the magnetic tape in the longitudinal direction thereof by utilizing a stationary head. On the other hand, in order to record and reproduce an audio signal of high quality, the deep layer audio recording and reproducing system has been employed, in which, after a frequency modulated audio signal (referred to as simply "FM audio signal", hereinafter) is recorded in a deep portion of slant tracks on a magnetic tape by using rotary audio heads mounted preceeding to rotary video heads, a video signal is recorded in a surface portion of the slanted tracks on the tape by using the rotary video heads.
During a reproducing operation of the deep layer audio recording and reproducing system, it is determined, by detecting a level of signal obtained from the rotary audio heads, whether or not the FM audio signal is recorded on the magnetic tape. That is, when the level is low enough, it is determined that there is no FM audio signal recorded on the magnetic tape and, when the level is high enough, it is determined that there is an FM audio signal recorded on the tape. Incidentally, since the azimuth angle of the rotary audio heads is different from that of the rotary video heads, the rotary audio heads do not reproduce a video signal recorded on the magnetic tape and thus the video signal is not erroneously determined as an FM audio signal.
On the other hand, an analog/digital VTR for recording and reproducing a digital signal in addition to an analog video and audio signals can be realized by simply making a tape speed and a track pattern for the digital signal the same as those of the VHS or 8 mm vide system. In such case, since there may be a case where only analog signals are recorded on a magnetic tape by the analog/digital VTR, it is required, necessarily, that the magnetic tape on which the analog signals are recorded by the analog/digital VTR can be reproduced by a conventional VTR.
However, when a magnetic tape on which a digital signal is recorded by the analog/digital VTR is reproduced by the conventional VTR, there may be a case where the conventional VTR erroneously determines a frequency spectrum of the reproduced digital information signal signal as a spectrum of a reproduced FM audio signal and produces an audio output with large noise, since the frequency spectrum of digital signal is distributed over a wide frequency band covering a frequency band of the reproduced FM audio signal.